Baffle assembly for ultrasonic liquid level measuring probe

Abstract: A baffle assembly (10) for use in an ultrasonic system for measuring the level of a contained volume of liquid by calculating the density of the liquid by means including the determination of the dielectric constant thereof. The baffle assembly (10) is located at the lower end of the stillwell (13) located within the volume of liquid. The assembly includes a pair of concentric sleeves (15,16) formed of electrically conductive material located to surround the lower end portion of the stillwell (13). The sleeves (15,16) are uniformly radially spaced from one another so as to function as a capacitor so that the electrical capacitance between the respective opposed surfaces of the sleeves may be determined.

Description: The invention relates to an ultrasonic liquid level measuring device located in a tank for determining a level of a liquid contained in the tank, the device including a tube adapted to contain a column of the liquid for ultrasonic determination of the length of the column, the tube having a lower end portion having at least one opening to permit entry of the liquid into the tube, the device also comprising two members that comprise an electrically conductive material and that are electrically insulated from one another and from the tube and the tank so as to function as a capacitor, and means for determining the capacitance between the members. Such an ultrasonic liquid level measuring device is known from US-A-4229798. In this known device, a plurality of holes are provided near a lower end of the tube. The members take the form of two arcuate plates located within the tube. The arcuate plates and the capacitance determining means function to detect the level of water lying below fuel, oil or petrol stored in the tank. It is desirable to provide a device in which the determination of the length of the column is improved. Additionally, some ultrasonic fuel measurement systems may require the determination of the fuel dielectric constant in order to calculate the density of the liquid. It is important to calculate fuel density on a continuous basis due to variations thereof that occur in response to temperature changes, changes in the velocity of sound and in the dielectric constant. Accordingly, these particular systems must utilize an electrical device or sensor to determine the dielectric constant. Such dielectric sensors are typically constructed of a number of concentric sleeves immersed in the liquid. The sleeves are formed of an electrically conductive material and are adapted to function as the plates of a capacitor. By determining the electrical capacitance between the opposed surfaces of the immersed concentric tubes, the dielectric constant can be calculated. It will be seen that these requirements, among others, dictate that a rather complex assembly be provided in order to properly utilize the tube (otherwise termed a "stillwell" or "probe") to obtain the fuel level measurements sought. According to the invention, therefore, the ultrasonic liquid level measuring device as first set forth above is characterised in that the two members are, respectively, first and second mutually concentric sleeves, each sleeve surrounding the tube lower end portion and having at least one radially extending opening for passage therethrough of the liquid, the capacitance determining means determining the capacitance between the respective opposed surfaces of the sleeves for determination of the dielectric constant of the liquid, the arrangement being such that the sleeves serve as baffles to prevent or reduce entry of air bubbles into the tube. The prevention or reduction of entry of air bubbles into the tube allows improved determination of the length of the column. Figure 1 is an elevational view of a baffle assembly located at the lower end of a stillwell in accordance with the invention, with parts broken away and shown in section for the purpose of illustration. Referring more particularly to the drawing, there is shown a baffle assembly 10 located on the floor of a fuel tank 11 which in the present embodiment may be considered the floor of an aircraft fuel tank. The fuel level in the tank is to be measured and displayed by means of an ultrasonic fuel level measuring system. The system utilizes an ultrasonic transducer for sending and receiving ultrasonic signals that are directed through the confined volume of fuel in the fuel tank. A part of this system is a tubular probe or stillwell 13 that is inserted approximately vertically in the tank. The stillwell 13 is provided with one or more radial openings 14 to permit fuel in the contained volume to freely enter. The purpose of the stillwell is to provide a liquid column that represents the level in the entire fuel tank but which is not subject to turbulence and other influences that could adversely effect the measurement. The ultrasonic transducer that is used in association with the stillwell is not shown, however, the use of such a device is well understood by those skilled in the art. The purpose of the bubble baffle assembly 10 as indicated above, is to prevent the entrance of gas bubbles into the fluid filled column within the stillwell 13. This reduces the possibility that bubbles in the fuel-filled column could influence the measurements obtained utilizing the ultrasonic pulses which are transmitted through the column. The baffle assembly 10 in the embodiment illustrated in Fig. 1, includes an outer cylindrical sleeve 15 and an inner cylindrical sleeve 16. In accordance with the invention, the sleeves 15 and 16 are formed of an electrically conductive material and are uniformly radially spaced from one another so that they may function as the plates of a capacitor. The sleeves 15 and 16 are mounted concentrically around the stillwell 13 by means of an annular upper seal ring 17 and an annular lower seal ring 18. The seal rings 17 and 18, are formed of a dielectric material to provide electrical insulation. The sleeves are spaced from one another by means of an annular upper spacer rib 21 formed on the downwardly facing surface of the upper seal ring 17 and by an annular lower spacer rib 22 formed integrally with and extending upwardly from the surface of the lower seal ring 18. The upper seal ring engages the surface of the stillwell 13 so that the annular spaces defined within the baffle assembly 10 are closed at the top except for vent openings to allow cumulated bubbles to escape. Fuel in the surrounding volume may enter the interior of the baffle assembly through radial openings 23 formed in the outer sleeve 15 and offset radial openings 24 formed in the inner sleeve 16. This produces a baffle effect that minimizes the possibility that bubbles generated during aerial maneuvers or during refueling will enter the stillwell 13. Additional sleeves may be added to increase the baffling effect or increase the capacitance of the dielectric sensor or both. As indicated above, the lower end of the stillwell 13 and the transducer are located within the bubble baffle structure in order to achieve the results described above. This arrangement also provides an advantageous means for force distribution to protect tank integrity during a crash. In accordance with the present invention, the baffle assembly 10, not only serves the baffling function described above but also functions to provide a capacitor that is used to measure the fuel dielectric constant. The measurement is obtained by circuit means connected to the sleeves 15 and 16 in such a way that the sleeves act as the plates of a capacitor that forms part of a dielectric sensor. The measurement thus obtained, is utilized together with other measurements such as the temperature of the fuel and the velocity of sound, to determine the fuel density. This data is then used in conjunction with the measurements obtained by the ultrasonic fuel level measuring system to determine the mass of fuel with a high degree of accuracy. While the invention has been shown and described with respect to a specific embodiment thereof, this is intended for the purpose of illustration rather than limitation and other variations and modifications of the specific device herein shown and described will be apparent to those skilled in the art all within the intended spirit and scope of the invention. Accordingly, the patent is not to be limited in scope and effect to the specific embodiment herein shown and described nor in any other way that is inconsistent with the extent to which the progress in the art has been advanced by the invention.

Claims: An ultrasonic liquid level measuring device located in a tank (11) for determining a level of a liquid contained in the tank (11), the device including a tube (13) adapted to contain a column of the liquid for ultrasonic determination of the length of the column, the tube (13) having a lower end portion having at least one opening to permit entry of the liquid into the tube (13), the device also comprising two members (15, 16) that comprise an electrically conductive material and that are electrically insulated from one another and from the tube (13) and the tank (11) so as to function as a capacitor, and means for determining the capacitance between the members (15, 16), characterised in that the two members are, respectively, first and second mutually concentric sleeves (15, 16), each sleeve (15, 16) surrounding the tube lower end portion and having at least one radially extending opening for passage therethrough of the liquid, the capacitance determining means determining the capacitance between the respective opposed surfaces of the sleeves (15, 16) for determination of the dielectric constant of the liquid, the arrangement being such that the sleeves (15, 16) serve as baffles to prevent or reduce entry of air bubbles into the tube (13). The device of claim 1, characterised in that the tube (13) is located approximately perpendicular to the surface of the contained volume of liquid and the sleeves (15, 16) are concentric with the axis of the tube. The device of claim 2, characterised in that an ultrasonic pulse is transmitted along the axis of the tube (13) through the column of the liquid. The device of claim 2, characterised in that the liquid (15) is contained in an aircraft fuel tank (11) and the sleeves (15, 16) and tube (13) are mounted on the floor of the fuel tank (11). The device of claim 1, characterised in that the means for determining the capacitance between the sleeves (15, 16) is adapted to determine the dielectric constant of the liquid. The device of claim 1, characterised in that the dielectric constant of the liquid is used to calculate the density of the liquid.

Inventors: BIRKETT ROBERT E, BIRKETT, ROBERT E.
Applicants: SIMMONDS PRECISION PRODUCTS, SIMMONDS PRECISION PRODUCTS INC.
Application year: 1994
Main classification: G01F23
IPC codes: G01F23